In an inner-focusing compact zoom lens, a varied ratio of a displacement of a focusing lens is greater in a close-up range, and in order to enhance a close-up performance with a single focusing cam scheme, a shift of the focal point becomes variably greater in the remaining zoom ranges where the lens behaves like a so-called vari-focal lens. A focusing cam curve useful to convert a vari-focal property to accommodate the zoom ranges must be prepared with appropriate adjustment of zooming parameters in relation with focusing parameters. Concentrating on the smooth zooming and focusing, it is hard to ensure a well-balanced cam configuration, and a revolving angle of the focusing cam must be varied, or some other corrections of the focusing cam are required.
In the prior art compact high-ratio zoom lens, the focusing lens is displaced while being revolved during both the zooming and the focusing. Guide grooves for rotational manipulations of a focusing cam barrel are engraved to support a cam mechanism; and the zooming causes operation pins fitting in the guide grooves to slide along the same so as to manipulatively rotate the focusing cam barrel. Thus, during the zooming, the focusing lens can move by an appropriate displacement in the zoom range which is determined by a rotational deviation of an operative range given by the focusing cam mechanism (see Patent Document 1 listed below).
Another prior art compact zoom lens can attain a focusing displacement by virtue of a concentric arrangement of a focus correcting cam with a focusing cam (see Patent Document 2).
Still another prior art compact high-ratio zoom lens assumes a five-layer telescopic structure where first cam, second cam, linearly movable and third cam barrel members overlay a fixed barrel (see Patent Document 2).
Further another prior art compact high-ratio zoom lens is comprised of a first cam barrel member underlaying a fixed barrel, a linearly movable barrel member underlaying the first cam barrel member, a focusing cam barrel member underlaying the linearly movable barrel member, and a second cam barrel member overlaying the fixed barrel and rotatably connected with the first cam barrel member where 2nd-lens-group studs disposed in an inner surface of the focusing cam barrel member are “fitted in focusing cams of the focusing cam barrel member, second group focusing cams 81 attached to a 2nd-lens-group slidable frame 72 for a linearly movable barrel member 18, 2nd-lens-group guide cams for the linearly movable barrel member 18, and first longitudinal guide grooves 82 in a first cam barrel member of a first cam barrel 16” (see Patent Document 3).